This invention relates to a refrigerating system using an air cycle.
A conventional refrigerator operating on an air cycle is disclosed, for example, in xe2x80x9cShin-ban Reito-Kucho-Binran Dai-4-han Kiso-henxe2x80x9d pp. 45-48, published by Japan Society of Refrigerating and Air Conditioning Engineers. Alternatively, an air conditioning system using an air cycle is disclosed in Japanese Unexamined Patent Publication No. 5-238489. With recent growing concern of global environment, attention has been focused on the air cycle according to which refrigeration can be effected without the use of artificial synthetic refrigerant typified by flon refrigerant.
Specifically, the air conditioning system disclosed in the above publication includes a circuit with a construction in which an expander, a heat exchanger and a compressor are sequentially connected so as to operate on an air cycle. A primary air is taken as a working fluid for the air cycle into this circuit. The primary air taken thereinto is pressure-reduced to a sub-atmospheric pressure in the expander and thereby reaches a low temperature. The low-temperature primary air exchanges heat with a secondary air in the heat exchanger. The secondary air is cooled through the heat exchange, and the cooled secondary air is supplied to a room to cool it. The primary air having absorbed heat from the secondary air in the heat exchanger is compressed to an atmospheric pressure in the compressor and then discharged from the circuit.
Further, in the air conditioning system described above, the expander is formed of a turbine and the compressor is formed of a turbo-compressor. Each of impellers of the expander and compressor is coupled to each other through a turbine shaft. The turbine shaft is coupled to a motor, whereby the motor drives the compressor and expander. Furthermore, expansion work of the air during its expansion in the expander is recovered as a driving force for the compressor via the turbine shaft.
Problems to be Solved
In the system described in the above publication, the intake air is expanded in the expander as it is. Therefore, while the air expands in the expander, moisture condenses in the air. In other words, part of expansion work of the air during expansion is taken by the moisture as its heat of condensation. Accordingly, the system has the problem in that expansion work of the air in the expander cannot sufficiently be recovered. Also, such insufficient recovery of expansion work presents another problem of increasing power for driving the compressor and thereby resulting in a reduction of COP (coefficient of performance).
The present invention has been made in view of these problems and therefore has its object of enhancing the COP by reducing required power for air compression in a refrigerating system using an air cycle.
A first solution taken in the invention is directed to a refrigerating system for cooling a subject to be cooled. The system is provided with an air cycle part (11) for taking in a heat-absorbing air, reducing the pressure of the heat-absorbing air and compressing the heat-absorbing air having absorbed heat from the subject to be cooled after the pressure reduction thereof, and dehumidifying means (60) for dehumidifying the heat-absorbing air and then supplying the heat-absorbing air to the air cycle part (11).
A second solution taken in the invention is directed to a refrigerating system for cooling a subject to be cooled. The system is provided with: an air cycle part (11) including an expander (22) for taking in a heat-absorbing air and reducing the pressure of the heat-absorbing air, a heat absorbing section (30) in which the heat-absorbing air reduced in pressure in the expander (22) absorbs heat from the subject to be cooled, and a compressor (21) for compressing the heat-absorbing air having absorbed heat in the heat absorbing section (30); and dehumidifying means (60) for dehumidifying the heat-absorbing air and then supplying the heat-absorbing air to the expander (22) of the air cycle part (11).
A third solution taken in the invention is based on the first or second solution, and provided with an internal heat exchanger (15) for heat-exchanging the heat-absorbing air which has been dehumidified in the dehumidifying means (60) and is being supplied to the air cycle part (11) with the heat-absorbing air in reduced pressure condition having absorbed heat from the subject to be cooled.
A fourth solution taken in the invention is based on the third solution, wherein the internal heat exchanger (15) is arranged to supply moisture to the heat-absorbing air in reduced pressure condition having absorbed heat from the subject to be cooled and use latent heat of evaporation of the moisture to cool the heat-absorbing air being supplied to the air cycle part (11).
A fifth solution taken in the invention is based on any one of the first to fourth solutions and provided with humidifying/cooling means (90) for cooling by humidification the heat-absorbing air reduced in pressure in the air cycle part (11), wherein the air cycle part (11) is arranged so that the heat-absorbing air cooled in the humidifying/cooling means (90) absorbs heat from the subject to be cooled.
A sixth solution taken in the invention is based on any one of the first to fifth solutions, wherein the air cycle part (11) is arranged to supply moisture to the heat-absorbing air absorbing heat from the subject to be cooled and use latent heat of evaporation of the moisture for heat absorption from the subject to be cooled.
A seventh solution taken in the invention is based on any one of the first to sixth solutions, wherein the air cycle part (11) is arranged to provide heat absorption from an air to be cooled as the subject to be cooled, supply moisture having condensed in the air to be cooled to the heat-absorbing air absorbing heat from the air to be cooled and use latent heat of evaporation of the moisture for heat absorption from the air to be cooled.
An eighth solution taken in the invention is based on the second solution, wherein the air cycle part (11) is arranged to provide heat absorption from an air to be cooled as the subject to be cooled in the heat absorbing section (30), and the heat absorbing section (30) is arranged to separate the air to be cooled from the heat-absorbing air by a moisture-permeable partition, supply moisture having condensed in the air to be cooled to the heat-absorbing air based on a pressure difference developed across the partition and use latent heat of evaporation of the moisture for heat absorption from the air to be cooled.
A ninth solution taken in the invention is based on any one of the first to eighth solutions and provided with water supply means (99) for supplying moisture to the heat-absorbing air so that the moisture evaporates in the heat-absorbing air being compressed in the air cycle part (11).
A tenth solution taken in the invention is based on any one of the first to ninth solutions, wherein the air cycle part (11) is arranged to operate in a mode of effecting an air cycle operation so that the heat-absorbing air in reduced pressure condition absorbs heat from the subject to be cooled and another mode in which the air cycle operation is stopped and the taken heat-absorbing air in normal pressure condition absorbs heat from the subject to be cooled.
An eleventh solution taken in the invention is based on any one of the first to tenth solutions, wherein the dehumidifying means (60) is arranged to include a humidity medium for effecting moisture absorption and release, dehumidify the heat-absorbing air through moisture absorption of the humidity medium and regenerate through moisture release of the humidity medium.
A twelfth solution taken in the invention is based on the eleventh solution, wherein the dehumidifying means (60) is arranged to release moisture to the heat-absorbing air compressed in the air cycle part (11).
A thirteenth solution taken in the invention is based on the twelfth solution, wherein the humidity medium of the dehumidifying means (60) is provided with a solid adsorbent for adsorbing moisture.
A fourteenth solution taken in the invention is based on the thirteenth solution, wherein the humidity medium of the dehumidifying means (60) is formed of a disc-shaped rotor member (61) which is formed to allow air passage in a direction of thickness thereof and brings the passing air into contact with the solid adsorbent, and the dehumidifying means (60) is provided with a moisture absorbing section (62) in which the rotor member (61) absorbs moisture from the heat-absorbing air passing through the rotor member (61), a moisture releasing section (63) in which the rotor member (61) releases moisture to the heat-absorbing air passing through the rotor member (61), and a drive mechanism for rotatively driving the rotor member (61) to allow the rotor member (61) to move between the moisture absorbing section (62) and the moisture releasing section (63).
A fifteenth solution taken in the invention is based on the twelfth solution, wherein the humidity medium of the dehumidifying means (60) comprises a liquid absorbent for absorbing moisture.
A sixteenth solution taken in the invention is based on the fifteenth solution, wherein the dehumidifying means (60) is arranged to heat the liquid absorbent with the heat-absorbing air compressed in the air cycle part (11) to release moisture from the liquid absorbent.
A seventeenth solution taken in the invention is based on the fifteenth solution, wherein the dehumidifying means (60) comprises a circulation circuit (64) that includes a moisture absorbing section (65) in which the liquid absorbent contacts with the heat-absorbing air to absorb moisture therefrom and a moisture releasing section (66) in which the liquid absorbent contacts with the heat-absorbing air to release moisture thereto, and that circulates the liquid absorbent between the moisture absorbing section (65) and the moisture releasing section (66).
An eighteenth solution taken in the invention is based on the eleventh solution and provided with heating means (101) for heating the heat-absorbing air compressed in the air cycle part (11) and then supplying the heat-absorbing air to the dehumidifying means (60).
A nineteenth solution taken in the invention is based on the eleventh solution and provided with heating means (101) for heating the heat-absorbing air immediately prior to being compressed in the air cycle part (11).
Operations
In the first solution, the dehumidifying means (60) dehumidifies the heat-absorbing air and then supplies it to the air cycle part (11). The air cycle part (11) takes in the dehumidified heat-absorbing air, and operates on an air cycle using this heat-absorbing air as a working fluid. Specifically, the air cycle part (11) reduces the pressure of the heat-absorbing air and then allows the heat-absorbing air reduced in pressure to absorb heat from the subject to be cooled. This heat absorption provides cooling of the subject to be cooled. The heat-absorbing air having absorbed heat is compressed and then discharged from the air cycle part (11). Since the heat-absorbing air taken in by the air cycle part (11) has previously been dehumidified, the heat-absorbing air does not cause moisture condensation when it is being expanded.
In the second solution, the dehumidifying means (60) dehumidifies the heat-absorbing air and then supplies it to the air cycle part (11). The air cycle part (11) takes in the dehumidified heat-absorbing air, and operates on an air cycle using this heat-absorbing air as a working fluid. Specifically, the heat-absorbing air is reduced in pressure in the expander (22). The heat absorbing section (30) allows the heat-absorbing air reduced in pressure to absorb heat from the subject to be cooled. This heat absorption provides cooling of the subject to be cooled. In the compressor (21), the heat-absorbing air having absorbed heat in the heat absorbing section (30) is compressed. The compressed heat-absorbing air is discharged from the air cycle part (11) Since the heat-absorbing air taken in by the air cycle part (11) has previously been dehumidified, the heat-absorbing air does not cause moisture condensation when it is being expanded in the expander (22).
In the third solution, heat exchange is made, in the internal heat exchanger (15), between the heat-absorbing air prior to being supplied to the air cycle part (11) and the heat-absorbing air brought into reduced pressure condition in the air cycle part (11). Though the heat-absorbing air reduced in pressure in the air cycle part (11) absorbs heat from the subject to be cooled, in some cases it still has a lower temperature after heat absorption than that as it had before being supplied to the air cycle part (11). In such cases, the heat exchange in the internal heat exchanger (15) provides reduction in temperature of the heat-absorbing air which will be supplied to the air cycle part (11).
In the fourth solution, moisture is supplied to the heat-absorbing air in reduced pressure condition in the internal heat exchanger (15). The supplied moisture evaporates through heat absorption from the heat-absorbing air prior to being supplied to the air cycle part (11). In other words, latent heat of evaporation of the moisture is used to cool the heat-absorbing air prior to being supplied to the air cycle part (11).
In the fifth solution, the humidifying/cooling means (90) supplies moisture to the heat-absorbing air reduced in pressure in the air cycle part (11). In this case, since the heat-absorbing air has already been humidified in the dehumidifying means (60), it will not be a saturated air even after it is expanded. Accordingly, the moisture evaporates in the heat-absorbing air so that the heat-absorbing air is cooled. In other words, the heat-absorbing air is reduced in temperature through its expansion and then further cooled by the humidifying/cooling means (90). Thereafter, the heat-absorbing air absorbs heat from the subject to be cooled.
In the sixth solution, moisture is supplied to the heat-absorbing air which is absorbing heat from the subject to be cooled in the air cycle part (11). The supplied moisture evaporates through heat absorption from the subject to be cooled. In other words, in the air cycle part (11), both the heat-absorbing air reduced in pressure and the moisture supplied to this heat-absorbing air absorb heat from the subject to be cooled, i.e., latent heat of evaporation of the moisture is also used to cool the subject to be cooled.
In the seventh solution, the air to be cooled is cooled as the subject to be cooled. In the cooled air to be cooled, moisture condenses into a drain. The air cycle part (11) supplies the drain to the heat-absorbing air which has been reduced in pressure and is now absorbing heat from the air to be cooled. The supplied drain evaporates in the heat-absorbing air through heat absorption from the air to be cooled. In other words, in the air cycle part (11), both the heat-absorbing air reduced in pressure and the drain supplied to this heat-absorbing air absorb heat from the air to be cooled, i.e., latent heat of evaporation of the drain is also used to cool the air to be cooled.
In the eighth solution, the air to be cooled is cooled as the subject to be cooled. Specifically, heat exchange is made, in the heat absorbing section (30), between the heat-absorbing air and the air to be cooled with the partition interposed therebetween. In the cooled air to be cooled, moisture condenses into a drain. In the heat absorbing section (30), the heat-absorbing air is in reduced pressure condition, while the air to be cooled is in normal pressure condition. Therefore, the drain permeates the partition due to a pressure difference across the partition and is thereby supplied to the heat-absorbing air in reduced pressure condition.
The supplied drain evaporates in the heat-absorbing air through heat absorption from the air to be cooled. In other words, in the heat absorbing section (30), both the heat-absorbing air reduced in pressure and the drain supplied to the heat-absorbing air absorb heat from the air to be cooled, i.e., latent heat of evaporation of the drain is also used to cool the air to be cooled.
In the ninth solution, the water supply means (99) supplies moisture to the heat-absorbing air. The moisture evaporates in the heat-absorbing air which is being compressed in the air cycle part (11). This moisture evaporation provides reduction in enthalpy of the heat-absorbing air after having been compressed.
In the tenth solution, the system operates in the mode of effecting an air cycle operation and the mode of stopping the air cycle operation. In the former mode, the air cycle part (11) takes in the heat-absorbing air and reduces the pressure thereof, and the heat-absorbing air reduced in pressure absorbs heat from the subject to be cooled. In the latter mode, the air cycle part (11) takes in the heat-absorbing air, and the taken heat-absorbing air absorbs heat from the subject to be cooled without being reduced in pressure.
The mode of stopping the air cycle operation is carried out in the following case. For example, the air cycle part (11) may take in the outdoor air as the heat-absorbing air. Therefore, in conditions where the outside air temperature is low, for example, in winter, cooling the subject to be cooled can often be implemented by using the low-temperature outside air alone without effecting the air cycle operation. Therefore, in such operating conditions, cooling the subject to be cooled is made with the air cycle operation stopped.
In the eleventh solution, the humidity medium of the dehumidifying means (60) absorbs moisture from the heat-absorbing air so that the heat-absorbing air is dehumidified. Further, the humidity medium releases moisture absorbed from the heat-absorbing air. This moisture release provides regeneration of the humidity medium. The regenerated humidity medium absorbs moisture from the heat-absorbing air again.
In the twelfth solution, the humidity medium of the dehumidifying means (60) releases moisture to the heat-absorbing air compressed in the air cycle part (11). This heat-absorbing air is at a high temperature as a result of heat absorption and compression in the air cycle part (11). Accordingly, the humidity medium releases moisture to the high-temperature heat-absorbing air and is thereby regenerated.
In the thirteenth solution, the humidity medium absorbs moisture in a manner that the moisture is adsorbed on the solid adsorbent. Further, the humidity medium releases moisture in a manner that the moisture is desorbed from the solid adsorbent.
In the fourteenth solution, the humidity medium is formed of a disc-shaped rotor member (61). A portion of the rotor member (61) absorbs moisture through contact with the heat-absorbing air in the moisture absorbing section (62). The rotor member (61) is rotatively driven by the drive mechanism so that the portion of the rotor member (61) having absorbed moisture moves to the moisture releasing section (63). In the moisture releasing section (63), the rotor member (61) releases moisture through contact with the heat-absorbing air coming from the air cycle part (11). The rotor member (61) as the humidity medium is thereby regenerated. Thereafter, the regenerated portion of the rotor member (61) moves to the moisture absorbing section (62) again and repeats these actions.
In the fifteenth solution, the humidity medium absorbs moisture in such a manner that the moisture is absorbed in the liquid absorbent. Further, the humidity medium releases moisture in such a manner that the moisture is desorbed from the liquid absorbent.
In the sixteenth solution, the liquid absorbent absorbs moisture from the heat-absorbing air not yet supplied to the air cycle part (11). This liquid absorbent is heated up into an easy-to-release condition by the heat-absorbing air of high temperature compressed in the air cycle part (11), and then released to the heat-absorbing air. This moisture release provides regeneration of the liquid absorbent.
In the seventeenth solution, the liquid absorbent absorbs moisture of the heat-absorbing air in the moisture absorbing section (65), whereby the heat-absorbing air is dehumidified. This liquid absorbent flows through the circulation circuit (64) to reach the moisture releasing section (66). In the moisture releasing section (66), the liquid absorbent releases moisture to the heat-absorbing air coming from the air cycle part (11), whereby the liquid absorbent is regenerated. The regenerated liquid absorbent flows through the circulation circuit (64) to reach the moisture absorbing section (65) again, and repeats this circulation. It is to be noted that in the moisture absorbing section (65) and moisture releasing section (66), the air and the liquid absorbent may be directly contacted with each other or may be indirectly contacted through a moisture permeable membrane or the like.
In the eighteenth solution, the heating means (101) heats the heat-absorbing air compressed in the air cycle part (11). In other words, the heat-absorbing air elevated in temperature by compression is further heated by the heating means (101) to raise its temperature. Thereafter, the heat-absorbing air is supplied to the dehumidifying means (60), and the humidity medium then releases moisture to the heat-absorbing air so as to be regenerated. In other words, the heat supplied to the heat-absorbing air by the heating means (101) is used to regenerate the humidity medium.
In the nineteenth solution, the heating means (101) heats the heat-absorbing air immediately prior to being compressed in the air cycle part (11). The heat-absorbing air heated by the heating means (101) is compressed and then supplied to the dehumidifying means (60). In other words, the heat-absorbing air previously elevated in temperature by heating in the heating means (101) is compressed to further raise its temperature. Then, in the dehumidifying means (60), the humidity medium releases moisture to the heat-absorbing air and is thereby generated. In other words, the heat supplied to the heat-absorbing air by the heating means (101) is used to regenerate the humidity medium.
Effects
According to the present invention, since the heat-absorbing air is dehumidified in advance by the dehumidifying means (60) and then expanded in the air cycle part (11), this prevents moisture condensation in the heat-absorbing air in the course of expansion. Accordingly, it can be avoided that expansion work during expansion of the heat-absorbing air is consumed by moisture condensation, which provides ensured recovery of expansion work. As a result, the recovered expansion work can be utilized for compression of the heat-absorbing air in the air cycle part (11). This reduces required power for compression to enhance the COP.
In the third and fourth solutions, the internal heat exchanger (15) is provided. Accordingly, if the heat-absorbing air after having absorbed heat has a lower temperature than that as it had before expanding, the heat-absorbing air before expanding can be cooled through heat exchange between both the heat-absorbing airs. Therefore, the heat-absorbing air before expanding can be reduced in temperature. In particular, according to the fourth solution, latent heat of evaporation of the moisture can be used to cool the heat-absorbing air before expanding, thereby further reducing the temperature of the heat-absorbing air. As a result, power required for compression of the heat-absorbing air can be reduced and the COP can be further enhanced.
According to the fifth solution, after having been reduced in temperature by expansion, the heat-absorbing air can be further cooled by the humidifying/cooling means (90). And, the heat-absorbing air thus cooled can be used to cool the subject to be cooled. According to the sixth, seventh and eighth solutions, moisture can be supplied to the heat-absorbing air which is absorbing heat from the subject to be cooled. And, latent heat of evaporation of the moisture can be used to cool the subject to be cooled. Therefore, according to each of these solutions, the cooling capacity can be improved merely by moisture supply without increasing required power for compression of the heat-absorbing air. Accordingly, the improvement in cooling capacity provides enhancement in the COP.
Further, according to the seventh and eighth solutions, a drain produced in the air to be cooled as the subject to be cooled can be supplied to the heat-absorbing air, and latent heat of evaporation of the drain can be used to cool the air to be cooled. This eliminates the need for the process of disposing of the drain produced by cooling the air to be cooled, thereby providing simplified construction.
According to the ninth solution, since moisture in the heat-absorbing air in the course of compression is evaporated, the enthalpy of the heat-absorbing air after having been compressed can be reduced. Therefore, an enthalpy differential can be reduced between both the heat-absorbing airs before and after compression, which enables reduction in power required for compression. Accordingly, according to this solution, the COP can be further enhanced.
According to the tenth solution, if the subject to be cooled can be sufficiently cooled without the effecting of the air cycle operation, the system can operate in the mode of stopping the air cycle operation. Therefore, unnecessary air cycle operations can be avoided, which enables reduction in energy required for cooling the subject to be cooled.
According to each of the eleventh to seventeenth solutions, the dehumidifying means (60) can be formed using the humidity medium for providing moisture absorption and release. In particular, according to the twelfth solution, energy possessed by the heat-absorbing air of high temperature coming from the air cycle part (11) can be used to regenerate the humidity medium, thereby providing effective use of energy. Further, according to the thirteenth to seventeenth solutions, the structure of the dehumidifying means (60) can be specified by using the humidity medium such as a solid adsorbent or a liquid absorbent.
According to the eighteenth and nineteenth solutions, heat supplied to the heat-absorbing air by the heating means (101) can be used to regenerate the humidity medium. In this respect, in order to ensure regeneration of the humidity medium, it is necessary to sufficiently elevate the temperature of the heat-absorbing air being supplied from the air cycle part (11) to the dehumidifying means (60) to reduce the relative humidity of the heat-absorbing air. In each of the above embodiments, however, the heat-absorbing air can be heated by the heating means (101). Therefore, the compression ratio of the heat-absorbing air in the air cycle part (11) can be reduced to a small value, while the temperature of the heat-absorbing air after having been compressed can be maintained. Accordingly, the system can reduce required power for compression of the heat-absorbing air while sufficiently regenerating the humidity medium, thereby providing enhancement in the COP.